aboutsummaryrefslogtreecommitdiff
path: root/driver/lexer.go
blob: 710d54d476d16d3954a55331cb5f37e5adda1513 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
package driver

import (
	"fmt"
	"io"
	"io/ioutil"

	"github.com/nihei9/maleeni/compiler"
)

type Token struct {
	ID      int
	Match   []byte
	EOF     bool
	Invalid bool
}

func newToken(id int, match []byte) *Token {
	return &Token{
		ID:    id,
		Match: match,
	}
}

func newEOFToken() *Token {
	return &Token{
		ID:  0,
		EOF: true,
	}
}

func newInvalidToken(match []byte) *Token {
	return &Token{
		ID:      0,
		Match:   match,
		Invalid: true,
	}
}

type lexer struct {
	tranTab *compiler.TransitionTable
	src     []byte
	srcPtr  int
	tokBuf  []*Token
}

func NewLexer(tranTab *compiler.TransitionTable, src io.Reader) (*lexer, error) {
	b, err := ioutil.ReadAll(src)
	if err != nil {
		return nil, err
	}
	return &lexer{
		tranTab: tranTab,
		src:     b,
		srcPtr:  0,
	}, nil
}

func (l *lexer) Next() (*Token, error) {
	if len(l.tokBuf) > 0 {
		tok := l.tokBuf[0]
		l.tokBuf = l.tokBuf[1:]
		return tok, nil
	}

	tok, err := l.next()
	if err != nil {
		return nil, err
	}
	if !tok.Invalid {
		return tok, nil
	}
	errTok := tok
	for {
		tok, err = l.next()
		if err != nil {
			return nil, err
		}
		if !tok.Invalid {
			break
		}
		errTok.Match = append(errTok.Match, tok.Match...)
	}
	l.tokBuf = append(l.tokBuf, tok)
	return errTok, nil
}

func (l *lexer) Peek1() (*Token, error) {
	return l.peekN(0)
}

func (l *lexer) Peek2() (*Token, error) {
	return l.peekN(1)
}

func (l *lexer) Peek3() (*Token, error) {
	return l.peekN(2)
}

func (l *lexer) peekN(n int) (*Token, error) {
	if n < 0 || n > 2 {
		return nil, fmt.Errorf("peekN() can handle only [0..2]")
	}
	for len(l.tokBuf) < n+1 {
		tok, err := l.next()
		if err != nil {
			return nil, err
		}
		l.tokBuf = append(l.tokBuf, tok)
	}
	return l.tokBuf[n], nil
}

func (l *lexer) next() (*Token, error) {
	state := l.tranTab.InitialState
	buf := []byte{}
	unfixedBufLen := 0
	var tok *Token
	for {
		v, eof := l.read()
		if eof {
			if tok != nil {
				l.unread(unfixedBufLen)
				return tok, nil
			}
			return newEOFToken(), nil
		}
		buf = append(buf, v)
		unfixedBufLen++
		entry := l.tranTab.Transition[state]
		if len(entry) == 0 {
			return nil, fmt.Errorf("no transition entry; state: %v", state)
		}
		nextState := entry[v]
		if nextState == 0 {
			if tok != nil {
				l.unread(unfixedBufLen)
				return tok, nil
			}
			return newInvalidToken(buf), nil
		}
		state = nextState
		id, ok := l.tranTab.AcceptingStates[state]
		if ok {
			tok = newToken(id, buf)
			unfixedBufLen = 0
		}
	}
}

func (l *lexer) read() (byte, bool) {
	if l.srcPtr >= len(l.src) {
		return 0, true
	}
	b := l.src[l.srcPtr]
	l.srcPtr++
	return b, false
}

func (l *lexer) unread(n int) {
	l.srcPtr -= n
}